Method of compacting metal powder into complicated shapes



" 7, 1943- P. SCHWARZKOPF 4 METHOD OF COMPACTING METAL POWDER INTOCOMPLICATED SHAPES 3 Sheets-Sheet 1 Filed June 6, 1944 INVENTOR. 7 PAULSCHWARZKOPF BY fl A Tram/FY P. SCHWARZKOP METHOD OF CONPA F ,7, CTINGMETAL POWDER INTO COHPLICATED SHAPES 3 Sheets-Sheet 2 Filed June 6, 1944PAUL SCHWARZKOPF BY L A TTORNE Y w: P. SCHWARZKOPF METHOD OF COIIPACTINGMETAL POWDER INTO COMPLICATED SHAPES Filed June 6, 1944 :s Sheets-Sheet3 INVENTOR. PAUL SCHWARZKOPF .BY

A TTOQNEY Patented Aug. 17, 1948 METHOD OF COMPACTING METAL POWDER INTOCOMPLICATED SHAPES Paul Schwarzkopf, Yonkers, N. Y., assignor toAmerican Electro Metal Corporation,

Yonkers,

N. Y., a corporation of Maryland Application June 6, 1944, Serial No.538,912

4 Claims. 1

This invention relates to the manufacture from powdery metallic materialof compacts and consolidated articles of rather complicated shape andparticularly provided with cit-sets, undercuts, recesses and/orprojections which may necessitate the use of split molds in shaping thepowder under pressure.

As is well known in the art of powder metallurgy, metallic powder ofsuitable particle size and in general between about 100 to less than onemicron average diameter of the individual particles, has flowcharacteristics which render it diflicult to compact the powder intoshapes of rather complicated configuration, such as provided with steps,undercuts, recesses and/or projections as exemplified by screw threads,threads and teeth. The pressure exerted upon the powder in the mold istranslated in the powder essentially in the direction of pressure and tofar smaller or no extent at an angle to it. Furthermore, the pressuretranslated into the powdery body diminishes both axially and laterallywith the distance from the pressing surface. Therefore, even in pressinga cylindrical body, the compression of the powder in the mold under thepunch is not uniform in that the compression is greatest in the centerand least at the sides, resulting in a kind of cone or parabolold ofhighest compression or particle concentration under the pressing surfaceof the punch. This flow characteristic of metallic powders can beimproved, but to a limited extent only, by the admixture of lubricantsto the powder which are volatile at temperatures below sinteringtemperature, such as paramn and compounds including stearic acid.

It is an object of the invention to facilitate or render it possible topress to shape metallic powders with or without admixed lubricants, intorather complicated shapes under which is understood herein and in theappended claims, a shape having off-sets, undercuts, projections and/orrecesses, and particularly shapes which necessitate the use of a splitmold.

It is another object of the invention to compact more uniformly thanheretofore possible, metallic powders into rather complicated shapes,and in particular in split molds.

It is still another object of the invention to compact metallic powdersinto rather complicated shapes so that the powder in projections, suchas threads or teeth extending in any direction, is compacted asuniformly as possible and forms a coherent mass in those projections.

It is a further object of the invention to compress both in axial andlateral direction, metallic powders into rather complicated shapes so asto obtain a compact which can be removed from the mold and handledthereafter without detericrating such as cracking or crumbling theprojectlons.

It is still a further object of the invention to compact metallicpowders particularly, but not exclusively, in a split mold into rathercomplicated shapes so that the compact is of an as uniform as possibledensity.

These and other objects of the invention will be more clearly understoodas the specification proceeds with reference to the drawings in whichFig. 1 shows by way of exemplification, in vertical cross section andpartly in elevation, a split mold for compacting a screw-threaded bodyfrom metallic powdery material and a punch used in a first stepaccording to the invention, Fig. 2 in elevation and on a smaller scale,the compacted body finally obtained, Fig. 3 in a similar manner as inFig. 1, a second step of the invention in its initial stage with aflexible and resilient. expans ble body inserted into the powdery masspressed or charged into the mold, Fig. 4 in s milar manner the secondstep of the invention in its final stage with the expans ble bodyinflated or expanded, Fig. 5 in a similar manner the removal of thedeflated, expansible body after completion of the second step of theinvention, Fig. 6 in similar manner the progress of a third step of theinvention with a punch pressing additonal material into the hollowcompact or shell, Fig. 7 in a similar manner the solid compact in themold after completion of the third step of the invention, Fig. 8 incross section and partly in elevation, a mold and a spiral gear shapecompacted therein, Fig. 9 a part-section through the spiral gear takenalong line 99 in Fig. 8, Fig. 10 a cross section through a part ofanother body of complicated shape compacted in a mold to form aspur-gear, Fig. 11 a modification of the invention, and Figs. 12 and 13another modification of the invention at the end of the first and startof the second step, respectively.

Referring to Fig. 1, I0 is a mold or die split along a vertical plane IIfor the production therein from powdery metallic material to which alubricant of the type mentioned hereinbefore may have been admixed, ifdesired, a hollow or solid body 4| screw-threaded on the outside asshown in Fig. 2 on a smaller scale. The mold cavity is formed by ascrew-threaded side face l2, which is the negative of the screw threadto Fig. 3.

be formed on the outside of the compact, and a bottom I 3 having acenter hole I 4. A preferably hollow and thin-walled metallic body lb ofslightly larger diameter than hole or bore i4 and having a downwardlytapering end i8 is fitted with the latter into hole l4. The radial orlateral distance between the outside of body 5 and a point furthest fromit in the side face I2 is such that lateral or radial pressure exertedthereafter upon the powder is translated uniformly through it. Thedesired metallic powder l1, e. g. of bronze, iron, steel, alloy steel ora mixture of steel and pure iron, is then fed in measured quantlty,'e.g. through one or more chutes 8 into the annular space between theoutside of body l5 and surfaces I2, I 3. After a predeterm ned amount ofmetal powder l9 has been deposited in the mold cavity, a ring-shapedpunch the lower pressing surface 2| of which tapers downwardly at asuitable angle, is lowered under pressure into the annular mold cavityso as to compress therein the powdery mass l9. The incline of pressureface 2| is such that the powdery mass I9 is displaced both downwardly aswell as laterally and thereby pressed in to the groove 22 to form thethread. After the first amount IQ of powder has thus been compacted to acertain degree or at predetermined compression ratio. punch 20 iswithdrawn and another amount of powder |'l fed into the annular moldcavity; thereupon punch 28 is lowered again under pressure. and thusalternating feeding of powder and compressing is continued until themold cavity it filled entirely with metallic powder which now forms ahollow pre-compacted body or shell 24, Fig. 3.

Hollow punch 20 is then moved laterally from the space above the openingof mold l0, and a flexible tube closed at its lower end or bag 23, forinstance of rubber, Fig, 3, is lowered into the hollow body I5 which isthereafter withdrawn upwardly. Alternatively and as it is assumed inFig. 3, body I5 is removed from the pre-compacted or tamped hollow body24 before bag 23 is introduced into hole 25; in order to preventcrumbling of surface layers around hole 25, bag 23 is slightly spacedfrom the latter as shown in A cylindrical support 26 for bottom 21 oftube or bag 23 is moved from below into bore l4. The upper end of bag 23is airor liquidtightly fitted into a member or bell 28, provided with ahollow nib 3|. A flexible duct 29, for instance a rubber or metal hose,Fig. 1, is connected with nib 3| and communicates through valve 30 witha source of compressed fluid, such as an air-compressor, a container forair or liquid under ressure, a water pump and the like. After tube orbag 23 has been lowered in any suitable manner into hole 25 of thetamped or 'precompacted body 24, fluid under pressure is admitted intobag 23 so as to forcibly expand it. Member or bell 28 is held inposition e. g. by mechanical means, such as a ram or lever (not shown),and bag 23 can expand under the pressure only laterally or radially intothe tamped or pre-compacted mass 24.

Fig. 4 shows the stage when the final pressure has been reached withinbag 23. Bag 23 translates the pressure upon the pre-compacted mass 24laterally or radially in the direction of arrows 32, and mass 24 willgive wherever it faces or is in the recess i2 and is less pre-compactedthan outside this recess. As a consequence, bulges 33 result in bag 23wherever it faces the threadrecess l2 in the mold ill. The pre-compactedpowder mass outside the recess is also compacted radially andadditionally.

In order to prevent the powder mass near the top of the mold cavity frombeing pressed upwardly by expanding tube 23, member 28 is provided witha flange 34 which completely covers and preferably projects beyond thefilling opening of the mold cavity into cylindrical recess 35, Fig. 4,and rests on shoulder 36.

After mass 24 is fully compacted to predetermined density and coherence,pressure is released from bag 23 for instance by turning valve 30 whichis 'a three-way valve. The deflated bag can be easily removed in themanner shown in Fig. 5. The cylindrical surface of hole 25 in thepre-compacted body 24, Fig. 3, is now changed to a kind of threadedsurface 31, and the innermost or smallest diameter of that surfacelarger than the diameter of hole 25 and of deflated bag 23.

If the flnally compacted shape 24 can be used for the ultimate purpose,the process according to the invention is now completed, and mold or diei0 can be opened by moving its parts or halves in the direction ofarrows 38, Fig. 5. A proper die holder for the split die I0 isconventional and not shown. Compact 24 is of sufficient density andcoherence so that it can be taken out of the opened mold and handledthereafter, particularly sintered in a proper furnace, for instance ofthe push furnace type.

If it is desired to produce a solid compact, the hollow compact 24 isleft in die ||i after bag 23 has been removed, Fig. 5, and support 26 islifted so that its upper surface is flush with bottom l3 of the diecavity, as shown in Fig. 6. Thereafter additional powdery material 39 isfilled into hole 31 of compact 24 and compressed by punch 40. Preferablyseveral measures of powdery material are successively fed into hole 31and tamped therein until it is filled entirely, Fig. 7, or topredetermined height, with powder preferably compacted to the samedensity as compact 24. A solid compact 4|, Fig. 7, threaded on theoutside is thus obtained. Split mold i0 is then opened and the compact4| removed, whereupon another cycle of operation can be started.

If a hollow or solid compact suitable for a spiral gear is to be made, asplit mold 42, Fig. 8, is used the cavity of which comprises recesses 43in which the spiral projections 44 are shaped. The method of compactingthe hollow or solid body 45 is otherwise the same as hereinbeforedescribed.

The utility of the invention is not limited, however, to compactingbodies from powdery initial material which are provided with lateralprojections such as screw-threads of various pitch, or result inundercuts which necessitate the use of a split mold. The invention isequally useful wherever the thickness of the body varies in a directionlateral or radial to that of the pressure which can be exerted upon thepowder in the mold cavity by one or more punches. If, for instance, acompact 49 suitable for a spurgear, Fig. 10, is to be pressed, the teeth41 of which are essentially parallel to the axis 48 of the body and thedirection of pressure exerted by punches lowered into the mold cavity,powder is filled and pro-compacted in cavity 46 so as to form first akind of shell therein. Then the flexible pressure means, such as arubber bag, is introduced into the cylindrical hole of the shell andpressure produced therein whereby the bag is inflated as shown in dottedlines 50 in Fig. 10; its bulges face the projections or teeth 91 andextend co-axially with axis 48 of the body. After shell 49 has beenfinally compacted, bag 59 is deflated and removed, and e. g. anothershell 52 compacted in shell 49 in a similar manher as the solid portion39 in Fig. 6.

From the above exemplifications of the invention it will be realizedthat it consists essentially in forming first in the mold cavity a kindof shell or hollow body from the powdery material, which ispre-compacted so as to increase its density. The thickness of the shellor hollow body measured in a direction lateral or perpendicular to thedirection of pre-compressing the powder in the mold, is chosen so thatin the subsequent step according to the invention in which a lateral orradial pressure is exerted, the latter is translated as uniformly aspossible through the powdery shell. Therefore, if the thickness of thehollow body to be compacted exceeds that which permits uniform lateralor radial compression according to the invention, the body is to besub-divided virtually into two or more co-axial or concentrical hollowbodies, the outermost of which is first compacted in the mannerhereinbeiore described, whereupon a second hollow body is compactedWithin the first one, and so on until either a hollow body of desiredthickness or a solid body is obtained.

Instead of using a solid or hollow body l5, inserted from above intomold l0, Fig. 1, according to the modification shown in Fig. 11, amandril or core rod 53 is raised through bore It into the position shownin full lines. After the powder has been filled into and compacted ortamped in the annular cavity between the surfaces l2, it and core rod 53in the manner described with reference to Fig. 1, to form apre-compacted shell 29, mandril 59 is lowered to the position shown indotted lines; preferably while mandril 53 is so lowered, the expansiblemeans 23 is introduced into the hole of shell 99 and rests on the uppersurface 59 of the mandril in its lowermost position.

Instead of using solid mandril 53, a tubular mandril 55, Fig. 12, can beused in the raised position of which the powdery material is filled intothe mold cavity to form the pre-compacted shell 29. The expansible meansor bag 23 is inserted into hollow mandril 55 at any time before thelatter is lowered into the position shown in Fig, 13, so that the means29 is in position within hole 25 when mandril 55 is so lowered. Asupport 59 fitting inside mandril 55 is moved into the position shown inFig. 13 so that the expansible means or bag 29 can rest on it (and onthe upper surface of mandril 55) during its subsequent expansion orinflation.

If a compact of rather complicated shape with projections and/orrecesses parallel to the axis of the mold cavity is produced accordingto the invention, for instance as described with reference to Fig. 10,either a split mold or a solid mold can be used. In the latter event,support 26, or a core rod, or a hollow mandril with inserted supportingrod, can also be used for ejecting the completed compact from the moldcavity.

The pressure to be exerted upon the powder by punch 29, Fig. 1, dependsupon the nature and particularly the flow-characteristics of the powderand may vary for instance between about 1 and 5 tons per square inch,though it may be higher as well known in the art. The lateral pressureexerted by the resilient pressure means 23 can be of similar or smallerorder, depending upon the strength of the bag. Since the latter issupported at its bottom and upon inflation pressed into the powder, itshould be clear that the finer the powder, the greater can be thepressure produced inside the bag and translated upon the powder withouttearing the bag. Instead of a bag of any suitable resilient material,other radially expansible means can be used, for instance alongitudinally split core member the complementary parts of which arewedge-shaped and can be displaced relative to one another in order toincrease the overall diameter of the core member. The core member canalso be composed of several sections which can be laterally displaced bya wedge member driven between them.

A compact completed according to the invention can be further densifiedand consolidated in any known manner, such as by subjecting it to fullsintering, or to a pre-sinter followed by repressing and a final sinter,or by final sintering under pressure. The sintered compact canthereafter be subjected to mechanical and/or heat treatment of any knownnature and effect, which is applicable to the metal, mixture and/oralloys of metals (which also may comprise a minor addition ofnon-metallic material) of which the compact consists.

What I claim is:

1. In a method of producing from metallic powder a cored article havingperipheral projections, the steps of providing a die cavity having arigid peripheral surface including recesses forming the negative ofmolded projections, providing a removable rigid core within said cavity,filling metalic powder into the space between the surfaces of saidcavity and core, exerting pressure in a direction essentially coaxialwith the core to preform a cored compact, replacing the core by aradially expanslble pressure means, and expanding the latter radially toadditionally and uniformly compress the preformed powder compact.

2. In a method set forth in claim 1, providing a hollow removable corewithin the die cavity, inserting the radially expansible pressure meansin the hole of said core, removing the hollow core after preforming thecored compact. and expanding thereafter said pressure means.

3. In a method as forth in claim 1, removing the expansible pressuremeans from the hole of the cored compact, filling into said hole anotherlayer of metallic powder, and compacting said layer within said hole.

4. In a method as set forth in claim 3, compressing the layer ofmetallic powder in the hole of the cored compact to a densityapproximating that of said cored compact.

PAUL SCHWARZKOPF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 720,718 Maddock Feb. 1'.. 19031,226,470 Coolidge May 15. 1917 1,321,125 Pfanstiehl Nov. 11, 19191,609,460 Buttles Dec. 7, 1928 2,313,227 De Bats Mar. 9, 1943 2,319,373Tormyn May 18, 1943 2,331,909 Hensel Oct. 19, 1943 2,299,192 Tormyn Oct.20, 1942 2,360,528 Talmage Oct. 17, 1944

